Fabricating highly integrated semiconductor devices needs highly miniaturized patterns. In order to integrate many elements within a small area, the individual elements must have small dimensions. The small dimensions can be achieved by reducing the pitch of a pattern, which is the sum of the width and the gap between adjacent patterns that are to be formed later. Currently, the drastic decrease of the design rules of semiconductor devices has reached a limit in terms of forming patterns at a fine pitch due to resolution restrictions of photolithography. In particular, if photolithography is used for forming a device isolation region that defines an active region in a substrate or for forming a line and space pattern (hereinafter referred to as “L/S pattern”), the forming of desired patterns at a fine pitch has reached a limit due to the resolution restrictions of photolithography.
In order to overcome the above-stated resolution restrictions of photolithography, methods of forming hardmask patterns at a fine pitch using double patterning have been suggested.
However, when a predetermined pattern is intended to be formed simultaneously in a region having a relatively high pattern density like a cell array region and a region having a relatively low pattern density like a peripheral circuit region or a core region, it is required to develop a double patterning of forming a desired pattern at different pitches for each region so that the double patterning can be selectively applied solely to the region having the higher pattern density.
Particularly, when the patterns at different pitches are simultaneously formed in respective regions having pattern densities different from each other, each region may have a different etch rate per region due to a difference of the pattern densities. Due to the different etch rates per region caused by the difference of the pattern densities, a film thickness that will be removed by subsequent etching may differ according to the pattern densities of respective regions. As a result, desired pattern shapes cannot be obtained due to the difference of the pattern densities in respective regions. Therefore, new double patterning methods, which can solve the problems possibly occurring when a film that is to be removed and has different thicknesses due to the pattern densities, are needed, particularly where predetermined patterns are intended to be simultaneously formed in a plurality of regions.